Method for preparing a complex of an aluminum alcoholate with aluminum and boron hydrides



2,903,471 Patented Sept. 8, 1 959 ice METHOD FOR PREPARING A COMPLEX OFAN ALCOHOLATE WITH AL M NUM .BORON HXDRIDES JanosKolionitsch,-Westfield,N.J-, assignor to Metal Hydrides Incorporated, Beverly, Mass,a corporation of Massachusetts .No Drawing. Application January 13, 1958Serial No. 708,403

Claims. (Cl. 260448) This invention relates to the preparation ofcomplexes of any aluminum alcoholate with aluminum and boron hydrideshaving the formula in which R, R and R are monovalent radicals selectedfrom the group consisting of alkyl, cycloalkyl, alkenyl, aralkyl or analkyl radical substituted with a halogen and in which R, R and R may bethe same or diiferent radicals.

These complexes are useful as reducing agents for reducing variousorganic and inorganic compounds, such as for reducing aldehydes tocarbinols, nitriles to amines and carboxylic acid esters to primarycarbinols. Some of these complexes are crystalline or glassy solids andothers are liquids with a tendency to supercooling. They are stablecompounds and are soluble in a variety of solvents, such as diethylether, benzene, hexane, chloroform, carbon tetrachloride andtetrahydrofuran, the solubility varying with the specific complex andspecific solvent. The thermal stability of these compounds varies, somebeing distillable while others decompose before reaching thedistillation temperature.

One method for preparing these compounds is described in my co-pendingapplication Serial No. 683,953, filed September 16, 1957. In accordancewith this method aluminum hydride is reacted with an ester of boric acidin a liquid carrier at a temperature below the temperature at whichaluminum hydride decomposes, the preferred temperature being between 0C. and normal room temperature. The reaction is illustrated by thereaction of aluminum hydride with methyl borate as shown by theequation:

One or more moles of methyl borate in the above equation may be replacedby the boric acid ester of a diflerent alcohol.

The present invention provides another method for preparing the abovementioned complexes. In accordance with the method of the presentinvention aluminum borohydride in the form of an etherate is reactedwith an aluminum alcoholate in a liquid carrier at a temperature belowthe temperature at which the aluminum borohydride etherate decomposes,the preferred temperature being between 0 C. and normal roomtemperature. The aluminum alcoholate may be selected from those havingthe formulas Al(OR) Al(OR Al(OR and mixtures thereof, where R, R and Rare monovalent radicals selected from the group consisting of.=alkyl,cycloalkyl, .alkylene, aralkyl, or an alkyl radical substituted with ahalogen and in which R,R and R may be the same or different radicals.The reactionisillustrated by the reaction of aluminum borohydride withaluminum methylate as shown by the equation:

In the preferred practice of the invention, the aluminum methylate inthe above equation may be replaced by another aluminum alkylate, amixture of aluminum ,allcylates, a mixed molecule aluminum alkylate ormixtures thereof. Suitable liquid carriers are theethers, such asdiethylether,tetrahydrdfuran, dibutyl ether or thefldlmethyl-or diethylethers of-the diethylene glyeols or mixtures of the ethers withhydrocarbon solvents, such as hexane, cyclohexane or benzene.

As illustrative of aluminum alcoholates which may be used in thepractice of the invention, I may mention aluminum ethylate,isopropylate, hexylate, methylate, npropylate, dimethylmonoisopropylate, n-butylate, tertiary butylate, secondary butylate,n-amylate, tertiary amylate, methyl isobutyl carbinylate, Z-heptylate,di-isopropyl carbinylate, n-octylate, 2,6,8-trimethyl-4-nonylate,allylate, oleylate, stearylate, 2-methyl-2,4-pentanediol alcoholate,benzylate, p-methyl benzylate, o-methyl benzylate, 2- phenylcyclohexylate, 1,3-dich1oro-2-propylate, cyclohexylate, cyclopentylatcand cycloheptylate.

The invention is illustrated further by the following specific examples.

Example 1 A solution of aluminum borohydride etherate of tetrahydroiuranwas prepared as follows. 13.5 grams of aluminum chloride, pulverized ina dry box, and 1.9 grams of powdered sodium borohydride were placed in a60 ml. round bottom flask. A receiver was filled with 15 ml. of drytetrahydrofuran. The apparatus was flushed out with dry nitrogen and thereactor was warmed up slowly to 130 C. At about C. a reaction commenced.The receiver was cooled with a Dry Ice-acetone bath. The reaction lastedabout 80 minutes. An active hydrogen determination on the resultingtetrahydrofuran solution showed that 0.5 ml. of solution liberated 60ml. of hydrogen. This is equivalent to 1800 ml. of hydrogen for thewhole solution or equal to 0.50 gram of aluminum borohydride. The yieldwas approximately 40 percent of theory.

This solution of 0.50 gram of aluminum borohydride was added to asolution of 5 grams of aluminum isopropylate in 30 ml. oftetrahydrofuran. The reaction mixture warmed up about 10 to 15 C. Aclear solution resulted. The tetrahydrofuran was pulled off by vacuumand the residue, which consisted of an oil and a white solid, wasdistilled under a pressure of about 1 mm. of mercury. 4.1 grams of acolorless, viscous oil was distilled at -125 C. Tests showed that thisproduct had the formula where R is isopropyl.

Example 2 17 grams of a product having the formula AlH (BH [Al(OCH 1 wasdissolved in 50 ml. of dry benzene and to this solution was added asolution of 16 grams of ethyl benzoate in 50 ml. of dry benzene. Thesolution was refluxed for 30 minutes. Then, 60 ml. of 5 N hydrochloricacid and 60 ml. of water was added. The benzene layer was washed with anaqueous sodium bicarbonate solution and again with water and then driedwith magnesium sulphate. The benzene was distilled off and the remainderfractionated under a pressure of 1 mm. Between 85 and 90 C., benzylalcohol was obtained with a yield of 77 percent of theoretical.

Iclaim:

l. The method for preparing complexes of aluminum alcoholates withaluminum and boron hydrides having the formula OR AIH3(BH A1 OR where R,R and R are monovalent radicals selected from the group consisting ofalkyl, cycloalkyl, alkenyl, aralkyl and an alkyl radical substitutedwith a halogen which comprises reacting an aluminum borohydride etheratewith an aluminum alcoholate in an ether-containing liquid carrier in theproportion of one mole of aluminum borohydride etherate to three molesof aluminum alcoholate, the aluminum alcoholate being selected from thegroup consisting of those having the formulas amount of an ethersufficient to form an etherate of aluminum borohydride.

References Cited in the file of this patent UNITED STATES PATENTS2,494,968 Schlesinger Jan. 17, 1950

1. THE METHOD FOR PREPARING COMPLEXES OF ALUMINUM ALCOHOLATES WITHALUMINUM AND BORON HYDRIDES HAVING THE FORMULA